The present invention relates to an improved process for the production of thiocarbohydrazide (TCH).
Several processes for the manufacture of thiocarbohydrazide (TCH) are known. TCH may be obtained during the hydrazinolysis of thiophosgene in an ether or water reaction medium in moderate yields. It is also known to manufacture TCH by hydrazinolysis of diethylxanthate.
It is also known to prepare thiocarbohydrazide through conversion of dialkyltrithiocarbonates with hydrazine. Cyclic trithiocarbonate may also be used for this synthesis.
The most common synthesis of thiocarbohydrazide is, however, the conversion of carbon disulfide with hydrazine. Hydrazinium-dithiocarbazinate (HDTC) forms according to equation (1): EQU CS.sub.2 +2H.sub.2 NNH.sub.2 .fwdarw.H.sub.2 NNHCSSH:NH.sub.2 NH.sub.2 ( 1).
This compound is then converted to thiocarbohydrazide with evolution of hydrogen sulfide according to equation (2): EQU H.sub.2 NNHCSSH.NH.sub.2 NH.sub.2 .fwdarw.H.sub.2 NNHCSNHNH.sub.2 +H.sub.2 S (2).
Better yields and pure product are obtained when the hot aqueous solution of the hydrazinium-dithiocarbazinate is digested with lead oxide (Stolle, et al., Ber. 41, 1099 (1908)).
The yields of thiocarbohydrazide can also be increased when conducting the decomposition of hydrazinium-dithiocarbazinate in aqueous solution in the presence of hydrazine (U.S. Pat. No. 2,726,263). It has been found that increasing the amount of water present in the hydrazine-containing reaction medium decreases the yield of TCH. The use of a water-free solvent for hydrazine (e.g., methyl, ethyl, or propyl alcohol), however, did not increase the TCH yield. In the process disclosed in U.S. Pat. No. 2,726,263, the hydrazinium-dithiocarbazinate (obtained in the usual way through conversion of carbon disulfide with hydrazine hydrate) is heated in an aqueous hydrazine solution at approximately 95.degree. C. for 1-2 hours under reflux. For each mole of hydrazinium-dithiocarbazinate, 1 to 3 moles of hydrazine are used. In a variation of this known process, carbon disulfide is cooled in an aqueous solution with 3 to 6 times the amount of hydrazine and is then heated. In both processes, the yield can be increased by repeatedly removing the TCH which forms during the course of the conversion from the reaction mixture. However, the yield is only 53.3% of theory.
It is also known to convert the hydrazinium-dithiocarbazinate thermally. Yields of approximately 70% of theory are obtained (Petri, Z. Naturforsch, 16B, 769 (1961)) in the thermal conversion process.
When TCH is produced by pyrolyzing a mixture of carbon disulfide and hydrazine hydrate, side reactions which result in the formation of ammonia and sulfur (and concomitant reduction in TCH yield) occur. These side reactions appear to be further catalyzed by the sulfur formed.
It would therefore be advantageous to develop a process for producing TCH from carbon disulfide and hydrazine in which the side reactions resulting in formation of ammonia and sulfur are suppressed.